Nowadays, a majority of apps require you to sign up with your email or even worse your phone number. If you have a phone number attached to your name, meaning you went to a cell service/phone provider, and you gave them your ID, then no matter what app you use, no matter how private it says it is, it is not private. There is NO exception to this. Your identity is instantly tied to that account.
Signal is not private. I recommend Simplex or another peer to peer onion messaging app. They don’t require email or phone number. So as long as you protect your IP you are anonymous
Yes that works if both the sender and receiever encrypt the emails before sending them.
I specifically mentioned incoming plaintext (unencrypted) email.
Since mail is technically decentralised, not everyone is using protonmail for example, so protonmail can only perform e2e encryption on protonmail to protonmail email sending (they let you encrypt mail to people outside but it’s not as seamless).
Nevertheless, I was mentioning incoming plaintext emails, which email providers have to encrypt before storing. The government can middleman that procedure and read the incoming mail before it’s encrypted by your provider (protonmail, etc).
(This is one of the reasons why lavabit may have shutdown, you can’t protect against incoming plaintext mail)